The present invention relates to semiconductor devices and, more particularly, to a method of forming a metal line of a semiconductor device employing a damascene scheme.
In recent years, a damascene scheme has been employed to form metal lines in semiconductor devices. The damascene metal line formation process includes forming a damascene pattern (such as a trench or contact hole) in an insulating layer, and then filling the damascene pattern with a metal material.
When a plug is formed using the damascene scheme, tungsten (W) is generally used as a conductive material. In the prior art, in the case where a tungsten plug is formed, it is difficult to lower the capacitance due to the narrow space between the metal lines present in a semiconductor device as the level of integration increases.
To solve the capacitance problem, there was a proposed method of reducing the capacitance value by decreasing the thickness of the conductive layer in an interconnection process. However, the resistance value is increased due to the thinned conductive layer.
To minimize the increase in resistance while lowering the capacitance, the interconnection process must be performed using a material having a low resistivity. Research has been performed regarding the interconnection process.
Materials having a low resistivity include copper (Cu), aluminum (Al) used as a wire material, and so on. The materials have been evaluated as materials to replace tungsten. Tungsten ha a resistivity of 6 μΩ·cm to 15 μΩ·cm, which is higher than the resistivity of aluminum: 2.7 μΩ·cm to 3.0 μΩ·cm. Accordingly, it is possible to maintain a low resistance while simultaneously lowering the height of the metal layer.
Although the plug or the metal line is formed using a conductive material having a low resistivity, the width of the plug or the metal line is decreased, thereby making it difficult to fill the contact hole with the conductive material. In particular, when aluminum is used to form the plug, the contact hole is not fully filled with aluminum since the gap-fill characteristics of aluminum are poor.
Chemical vapor deposition (CVD) is used to solve this problem. However, it is difficult to perform chemical mechanical polishing (CMP) for the shortage between lines. Furthermore, the properties of aluminum may be changed due to a thermal process carried out in a subsequent step because aluminum has a low melting point. Thus, there is a need for a method capable of solving these problems.